U.S. patent application number 16/076049 was filed with the patent office on 2019-12-19 for active mems microbeam device for gas detection.
This patent application is currently assigned to KING ABDULLAH UNIVERSITY OF SCIENCE AND TECHNOLOGY. The applicant listed for this patent is KING ABDULLAH UNIVERSITY OF SCIENCE AND TECHNOLOGY. Invention is credited to Adam BOUCHAALA, Nizar JABER, Mohammad YOUNIS.
Application Number | 20190383715 16/076049 |
Document ID | / |
Family ID | 58544995 |
Filed Date | 2019-12-19 |
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United States Patent
Application |
20190383715 |
Kind Code |
A1 |
BOUCHAALA; Adam ; et
al. |
December 19, 2019 |
ACTIVE MEMS MICROBEAM DEVICE FOR GAS DETECTION
Abstract
Sensors and active switches for applications in gas detection
and other fields are described. The devices are based on the
softening and hardening nonlinear response behaviors of
microelectromechanical systems (MEMS) clamped-clamped microbeams.
In that context, embodiments of gas-triggered MEMS microbeam
sensors and switches are described. The microbeam devices can be
coated with a Metal-Organic Framework to achieve high sensitivity.
For gas sensing, an amplitude-based tracking algorithm can be used
to quantify an amount of gas captured by the devices according to
frequency shift. Noise analysis is also conducted according to the
embodiments, which shows that the microbeam devices have high
stability against thermal noise. The microbeam devices are also
suitable for the generation of binary sensing information for
alarming, for example.
Inventors: |
BOUCHAALA; Adam; (Thuwal,
SA) ; JABER; Nizar; (Thuwal, SA) ; YOUNIS;
Mohammad; (Thuwal, SA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KING ABDULLAH UNIVERSITY OF SCIENCE AND TECHNOLOGY |
Thuwal |
|
SA |
|
|
Assignee: |
KING ABDULLAH UNIVERSITY OF SCIENCE
AND TECHNOLOGY
Thuwal
SA
KING ABDULLAH UNIVERSITY OF SCIENCE AND TECHNOLOGY
Thuwal
SA
|
Family ID: |
58544995 |
Appl. No.: |
16/076049 |
Filed: |
March 30, 2017 |
PCT Filed: |
March 30, 2017 |
PCT NO: |
PCT/IB2017/051837 |
371 Date: |
August 7, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62315966 |
Mar 31, 2016 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N 2291/015 20130101;
G01N 29/036 20130101; G01N 2291/0257 20130101; G01N 29/032
20130101; G01N 29/022 20130101; G01N 2291/0256 20130101; G01N 5/02
20130101 |
International
Class: |
G01N 5/02 20060101
G01N005/02; G01N 29/02 20060101 G01N029/02; G01N 29/036 20060101
G01N029/036 |
Claims
1. A system, comprising: a microelectromechanical system (MEMS)
microbeam device; an instrument to measure structural vibrations of
the MEMS microbeam device over time; and a processing circuit
coupled to the instrument and configured to: conduct an analysis of
the structural vibrations of the MEMS microbeam device; and detect
a change in a response behavior of the MEMS microbeam device based
on the analysis.
2. The system of claim 1, wherein the MEMS microbeam device is
coated with a Metal-Organic Framework (MOF) layer.
3. The system of claim 2, wherein the MOF layer comprises an
HKUST-1 MOF layer.
4. The system of claim 1, wherein the change in the response
behavior of the MEMS microbeam device comprises a mass-induced
change in the response behavior.
5. The system of claim 1, wherein the MEMS microbeam device is
operated at an operating pressure and at an operating voltage to
induce at least one of a softening nonlinear response behavior or a
hardening nonlinear response behavior of the MEMS microbeam
device.
6. The system of claim 1, wherein the processing circuit is further
configured to track a frequency response of the structural
vibrations of the MEMS microbeam device over time.
7. The system of claim 1, wherein the processing circuit is further
configured to quantify a mass captured by the MEMS microbeam device
based on a frequency shift of the structural vibrations of the MEMS
microbeam device over time.
8. The system of claim 1, wherein the processing circuit is further
configured to trigger a switch based on a difference in a frequency
response of the structural vibrations of the MEMS microbeam device
over time.
9. A method, comprising: operating a microelectromechanical system
(MEMS) microbeam device at an operating pressure and at an
operating voltage; measuring structural vibrations of the MEMS
microbeam device over time; conducting an analysis of the
structural vibrations of the MEMS microbeam device; and detecting a
change in a response behavior of the MEMS microbeam device based on
the analysis.
10. The method of claim 9, wherein the MEMS microbeam device is
coated with a Metal-Organic Framework (MOF) layer.
11. The method of claim 10, wherein the MOF layer comprises an
HKUST-1 MOF layer.
12. The method of claim 9, wherein the change in the response
behavior of the MEMS microbeam device comprises a mass-induced
change in the response behavior.
13. The method of claim 9, further comprising operating the MEMS
microbeam device to induce at least one of a softening nonlinear
response behavior or a hardening nonlinear response behavior of the
MEMS microbeam device.
14. The method of claim 9, further comprising tracking a frequency
response of the structural vibrations of the MEMS microbeam device
over time.
15. The method of claim 14, further comprising quantifying a mass
captured by the MEMS microbeam device based on a frequency shift of
the structural vibrations of the MEMS microbeam device over
time.
16. The method of claim 14, further comprising triggering a switch
based on a difference in a frequency response of the structural
vibrations of the MEMS microbeam device over time.
17. A method, comprising: forming a sacrificial layer over at least
one lower electrode, the sacrificial layer comprising anchor
passages extending through the sacrificial layer to the lower
electrode; forming an upper electrode on the sacrificial layer, the
upper electrode contacting the at least one lower electrode through
the anchor passages; forming a structural layer on the upper
electrode; forming a protective layer on the structural layer;
removing the sacrificial layer to release a microbeam comprising
the upper electrode, the structural layer and the protective layer,
the microbeam suspended by anchors defined by the anchor passages;
and coating the microbeam with a Metal-Organic Framework (MOF)
layer.
18. The method of claim 17, wherein the upper electrode comprises a
first chromium layer, a gold layer disposed on the first chromium
layer, and a second chromium layer disposed on the gold layer.
19. The method of claim 17, wherein the structural layer comprises
polyimide.
20. The method of claim 17, wherein the MOF layer comprises an
HKUST-1 MOF layer.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to, and the benefit of,
co-pending U.S. provisional application entitled "Active MEMS
Devices for Gas Detection" having Ser. No. 62/315,966, filed Mar.
31, 2016, which is hereby incorporated by reference in its
entirety.
BACKGROUND
[0002] Microelectromechanical systems (MEMS) are attractive for use
in various applications and fields due to their capabilities and
performance. MEMS sensors have broad uses among fields, such as
medicine, aerospace, automotive, public safety, and security. The
importance of small mass detection and measurement, for example,
has led to the development of sophisticated microstructure designs
with high sensitivity reaching femtogram resolution. The need for
accurate and highly sensitive microsensors has also led to cutting
edge research biology and chemistry to detect very small mass
quantities.
SUMMARY
[0003] According to the embodiments, electrostatically actuated
clamped-clamped microbeams coated with a sensitive chemical
Metal-Organic Framework (MOF) layer, such as HKUST-1 or another MOF
coating, act as a gas-triggered sensor or switch. The proposed
electromechanical device can work as both a sensor to track changes
in frequency before a sudden change in amplitude and as an
electrical switch (or actuator) activated upon gas adsorption
beyond certain threshold. A frequency shift is demonstrated that
can be tracked over a nonlinear regime using a linearly fitted
upper branch in hardening behavior. The quantity of mass attached
on the microbeam can be approximated using the responsivity of the
microbeam calculated in the linear regime. Empirical results
described herein include the mass threshold of an example
clamped-clamped microbeam.
[0004] As described in further detail below, clamped-clamped
microbeams can also be used to track frequency shift in real time
based on the amount of mass attached on the surface of the sensor.
The embodiments can track the frequency shift until reaching a
specific threshold to trigger a switch. In that context, a
clamped-clamped microbeam resonator can be electrically and/or
communicatively coupled to a microcontroller or other suitable
circuitry to perform frequency detection and switching quickly.
[0005] Other systems, methods, features, and advantages of the
present disclosure will be apparent to one having ordinary skill in
the art upon examination of the following drawings and detailed
description. It is intended that all such additional systems,
methods, features, and advantages be included within this
description, be within the scope of the present disclosure, and be
protected by the accompanying claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] For a more complete understanding of the embodiments
described herein and the advantages thereof, reference is now made
to the following description, in conjunction with the accompanying
figures briefly described below.
[0007] FIG. 1 illustrates an example rendering of an
electrostatically actuated clamped-clamped microbeam according to
various embodiments described herein.
[0008] FIG. 2A illustrates a microbeam fabrication process
according to various embodiments described herein.
[0009] FIG. 2B illustrates an optical image of an example microbeam
fabricated according to the process shown in FIG. 2A.
[0010] FIG. 3A illustrates a bottle of Cu.sub.3(btc).sub.2
metal-organic framework according to various embodiments described
herein.
[0011] FIG. 3B illustrates powder X-ray diffraction results
performed on the example microbeam shown in FIG. 2B after being
coated with the metal-organic framework shown in FIG. 3A.
[0012] FIGS. 4A-4C illustrate noise analysis graphs at a first
pressure, including conductance as a function of frequency, phase
as a function of frequency, and variation of phase at a fixed
frequency as a function of time, respectively, for an example
microbeam according to various embodiments described herein.
[0013] FIGS. 5A-5C illustrate noise analysis graphs at a second
pressure, including conductance as a function of frequency, phase
as a function of frequency, and variation of phase at a fixed
frequency as a function of time, respectively, for an example
microbeam according to various embodiments described herein.
[0014] FIGS. 6A and 6B illustrate frequency response curves of an
example microbeam for different DC voltages showing a transition
from a linear to a softening behavior at a first pressure and for
different AC voltages showing a transition from linear to hardening
behavior at a second pressure, respectively, according to various
embodiments described herein.
[0015] FIG. 7 illustrates an example diagram of a setup for optical
gas sensing according to various embodiments described herein.
[0016] FIGS. 8A and 8B illustrate real time measurements of a
frequency response jump before and after vapor exposure, including
a jump up at 3.3 Torr and a jump down at 220 mTorr, respectively,
according to various embodiments described herein.
[0017] FIGS. 9A and 9B illustrate frequency responses before and
after gas sensing and a linear fitting of the upper branch in the
frequency response at 220 mTorr, respectively, according to various
embodiments described herein.
[0018] FIGS. 10A and 10B illustrate real time amplitude variation
and frequency shift, respectively, as a function of time upon gas
exposure according to various embodiments described herein.
[0019] FIGS. 11A and 11B illustrate noise analysis graphs at a
first pressure, including conductance as a function of frequency
and phase as a function of frequency, respectively, according to
various embodiments described herein.
[0020] FIGS. 11C-11E illustrate noise analysis graphs, including
variation of phase at fixed frequencies of 91.11 kHz, 91.17 kHz,
and 91.21 kHz as a function of time, respectively, according to
various embodiments described herein.
[0021] FIG. 12 illustrates a real time measurement and
corresponding light emitting diode trigger according to various
embodiments described herein.
[0022] FIG. 13 illustrates another real time measurement and
corresponding light emitting diode trigger according to various
embodiments described herein.
[0023] The drawings illustrate only example embodiments and are
therefore not to be considered limiting of the scope described
herein, as other equally effective embodiments are within the scope
and spirit of this disclosure. The elements and features shown in
the drawings are not necessarily drawn to scale, emphasis instead
being placed upon clearly illustrating the principles of the
embodiments. Additionally, certain dimensions may be exaggerated to
help visually convey certain principles. Moreover, in the drawings,
similar reference numerals between figures designate like or
corresponding, but not necessarily the same, elements.
DETAILED DESCRIPTION
[0024] Sensors and active switches for applications in gas
detection and other fields are described. The devices are based on
the softening and hardening nonlinear response behaviors of
micro-machined clamped-clamped microbeams. In that context,
embodiments of gas-triggered microelectromechanical systems (MEMS)
microbeam sensors and switches are described. The microbeam devices
can be coated with a Metal-Organic Framework to achieve high
sensitivity. For gas sensing, an amplitude-based tracking algorithm
can be used to quantify an amount of gas captured by the devices
according to frequency shift. Noise analysis is also conducted
according to the embodiments, which shows that the microbeam
devices have high stability against thermal noise. The microbeam
devices are also suitable for the generation of binary sensing
information for alarming, for example.
[0025] FIG. 1 illustrates an example rendering of an
electrostatically actuated clamped-clamped microbeam 100 according
to various embodiments described herein. As to fabricating an
example microbeam similar to the microbeam 100, FIG. 2A illustrates
a microbeam fabrication process 200. Referring to FIG. 2A-1, the
process 200 starts with a silicon wafer 202 of suitable size (e.g.,
4, 6, 8, etc. inch silicon wafer). In FIG. 2A-2, a silicon dioxide
insulation layer 204 is deposited upon the silicon wafer 202. As
shown in FIG. 2A-3, the next step is to sputter a lower electrode
206, which can be composed of a layer of gold and chrome, among
other suitable metals, at a thicknesses of about 250 nm/50 nm.
Other metals and thicknesses can be used for the lower electrode in
various embodiments.
[0026] Next, as shown in FIG. 2A-4, amorphous silicon is deposited
on top of the layer of gold and chrome to form a sacrificial layer
208. Two anchors 210 are etched in the amorphous silicon layer to
connect the upper electrode with the lower connections as also
shown in FIG. 2A-4. In FIG. 2A-5, the upper electrode 212 is
fabricated with chrome/gold/chrome layers of thicknesses 50 nm/250
nm/50 nm, for example, although other suitable metals and/or
thicknesses can be used. Then, in FIG. 2A-6, 6 .mu.m of polyimide
214 is spun and cured at gradually increasing temperature from
150.degree. C. to 350.degree. C. in 50 minutes and then held at
350.degree. C. for 30 minutes to form a structural layer. In other
embodiments, other thicknesses of the polyimide 214 can be spun and
cured at other temperatures and over other periods of time. In FIG.
2A-7, a nickel layer 216 of suitable thickness (e.g., 500 nm) is
sputtered on the top surface of the polyimide 214 in order to
protect the microbeam during reactive ion etching. As shown in FIG.
2A-8, the sacrificial layer 208 is removed using reactive ion
etching or another suitable method.
[0027] The geometrical properties of an example microbeam
fabricated according to the process 200 shown in FIG. 2A are shown
below in Table 1, and FIG. 2B illustrates an optical image of an
example microbeam fabricated according to the process 200 shown in
FIG. 2A.
TABLE-US-00001 TABLE 1 Geometrical Properties of an Example
Microbeam Symbol Quantity Dimensions L Length 600 [.mu.m] H
Thickness 6.85 [.mu.m] B Width 50 [.mu.m]
[0028] In other aspects of the embodiments, a microbeam fabricated
according to the process 200 shown in FIG. 2A is coated with a MOF
solution. MOFs are compounds consisting of metal ions or clusters
coordinated to organic molecules to form one-, two-, or
three-dimensional structures that can be porous. In one embodiment,
a Cu.sub.3(btc).sub.2 MOF, where btc is
1,3,5-benzenetricarboxylate, also known as HKUST-1, is used for the
coating. The HKUST-1 can be prepared using the method described in
"Patterned Deposition of Metal-Organic Frameworks onto Plastic,
Paper, and Textile Substrates by Inkjet Printing of a Precursor
Solution," by Jin-Liang Zhuang, Deniz Ar, Xiu-Jun Yu, Jin-Xuan Liu,
and Andreas Terfort, Advanced Materials, Vol. 25 (2013) pp.
4631-4635, although other MOFs and methods of MOF preparation can
be relied upon among the embodiments.
[0029] FIG. 3A illustrates a bottle of Cu.sub.3(btc).sub.2 MOF,
also known as HKUST-1, according to various embodiments described
herein. The HKUST-1 has a light blue color due to the existence of
the ethylene glycol. The MOF solution can be useful for several
months after it has been prepared. In one embodiment, an inkjet
printer can be used to coat the microbeam shown in FIG. 3A (or
other microbeam or similar MEMS device) with the HKUST-1 MOF
solution. An inkjet printer having a nozzle of 20 .mu.m in
diameter, for example, can be used, although the nozzle can be
larger or smaller depending upon the desired thickness of the
HKUST-1 coating. To ensure the evaporation of the solvent in the
HKUST-1 and avoid shifting in real time measurements upon gas
exposure, the microbeam can also be exposed to a flow of nitrogen
for a sufficient time. In other embodiments, however, the nitrogen
exposure can be skipped or omitted. To confirm the existence of the
HKUST-1 on the surface of the microbeam, powder X-ray diffraction
(PXRD) was performed, and the results are shown in FIG. 3B.
[0030] As described in detail below, the HKUST-1-coated microbeam
can be used as a gas detector, sensor, and/or switch. To determine
the minimum detectable frequency and, thus, the minimum detectable
mass of the gas sensor at a given temperature, a noise analysis was
performed in different conditions. The frequency shift due to
thermal fluctuations around the resonator can be related to the
phase variation at a given frequency. In that context, an Agilent
4294A precision impedance analyzer, connected to a PC with a GPIB
interface from National Instruments, was used for data acquisition
to electrically characterize the microbeam.
[0031] FIGS. 4A-4C illustrate noise analysis graphs at a first
pressure, including conductance as a function of frequency, phase
as a function of frequency, and variation of phase at a fixed
frequency as a function of time, respectively, for an example
microbeam. More particularly, FIG. 4A illustrates conductance as a
function of frequency at 200 mTorr with VDC=1.5V and VAC=1V. The
constant excitation frequency is selected to be 90.23 kHz at the
middle of the linearly fitted (e.g., Lorentz fitted) zone in the
phase response curve in FIG. 4A, where the slope is found to be
equal to |d.PHI./df|=4.47 10.sup.-4[.degree./Hz]. FIG. 4B
illustrates phase as a function of frequency at 200 mTorr with
VDC=1.5V and VAC=1V. Finally, FIG. 4C illustrates variation of the
phase over time at the fixed frequency of 90.23 kHz. In other
words, FIG. 4C shows the phase evolution as a function of time at a
fixed frequency. The phase noise is calculated to be
d.PHI.=0.157.degree., which leads to a frequency shift of
.delta.f.sub.noise.sup.200 mTorr=d.PHI./|d.PHI./df|=351.23
[Hz].
[0032] FIGS. 5A-5C illustrate noise analysis graphs at a second
pressure, including conductance as a function of frequency, phase
as a function of frequency, and variation of phase at a fixed
frequency as a function of time, respectively, for an example
microbeam. More particularly, FIG. 5A illustrates conductance as a
function of frequency at 3.3 Torr with V.sub.DC=7V and V.sub.AC=1V.
The constant excitation frequency is selected to be 84.5 kHz at the
middle of the linearly fitted zone in the phase response curve in
FIG. 5A. FIG. 5B illustrates phase as a function of frequency at
3.3 Torr with VDC=7V and VAC=1V. Finally, FIG. 5C illustrates
variation of the phase over time at the fixed frequency of 84.5
kHz.
[0033] With regard to FIGS. 5A-5C, the same noise analysis
procedure detailed above with reference to FIGS. 4A-4C was
performed at a pressure of 3.3 Torr, which is another example
operating pressure for microbeam devices. Using linear fitting, the
slope of the linear branch in FIG. 5B was determined to be
|d.PHI./df|=7.65 10.sup.-4[.degree./Hz]. The phase variation for
the constant frequency of 84.5 kHz was determined to be
d.PHI.=0.159.degree., which leads to a frequency shift of
.delta.f.sub.noise.sup.3.3 Torr=d.PHI./df|=207.84 [Hz].
[0034] In order to determine the linear relation between the
induced frequency shift and mass added to the microbeam, the
responsivity of the microbeam sensor can be calculated as:
- 1 = d m df = 2 m eff f res , 0 V , ( 1 ) ##EQU00001##
where f.sub.res,0V=86.8 [kHz] is the natural resonant frequency at
V.sub.DC=0V and m.sub.eff is the effective mass of the microbeam
sensor represented as m.sub.eff=.alpha. m and .alpha.=0.3965 for
the first natural frequency of the microbeam. The mass of the
microbeam is m=510 [ng]. From Eq. (1), the responsivity of the
sensor is
1 st - 1 = 4.65 [ pg Hz ] . ##EQU00002##
[0035] Based on the calculated responsivity value, the minimum
detectable mass .delta.m.sub.noise can be calculated from the
minimum detectable frequency .delta.f.sub.noise due to thermal
fluctuations. Based on Eq. (1), the relation between
.delta.m.sub.noise and .delta.f.sub.noise can be written as
.delta.m.sub.noise=.sup.-1.delta.f.sub.noise. (2)
[0036] To further investigate the response of the coated microbeam,
frequency response curves are generated for various voltage loads.
A microbeam has two different sources of nonlinearities. The first
comes from mid-plane stretching due to the geometry of the
structure and the fixed anchors. This nonlinearity is cubic and is
dominant for low DC voltages, which leads to hardening behavior.
The second source of nonlinearity is due to the electrostatic
force, which is quadratic in nature, and leads to softening
behavior.
[0037] FIGS. 6A and 6B illustrate frequency response curves of an
example microbeam for different DC voltages showing a transition
from a linear to a softening behavior at a first pressure and for
different AC voltages showing a transition from linear to hardening
behavior at a second pressure, respectively, according to various
embodiments described herein. More particularly, FIG. 6A shows a
transition from a linear to a softening behavior at 3.3 Torr, and
FIG. 6B shows a transition from linear to hardening behavior for
different AC voltages at 220 mTorr.
[0038] The microbeam data shown in FIGS. 6A and 6B was captured at
the same conditions of the gas sensing experiments described below,
which is at a pressure of 3.3 Torr. In FIG. 6A, the black-square
curve represents the frequency response of the beam in the linear
regime. When increasing the DC voltage, softening behavior starts
to appear. At V.sub.DC=21V and V.sub.DC=0.5V, a jump of 0.3 .mu.m
occurs between two saddle-nodes. The jump can be utilized for a gas
switch trigger as described below. As described herein, this type
of response can be called a jump-up switch.
[0039] As shown in FIG. 6B, increasing the AC voltage with a lower
range of DC voltages leads to the appearance of the hardening
behavior (i.e., the electrostatic nonlinearity is weaker). The
advantage of a hardening frequency response curve is that, for a
certain voltage load, an almost linear segment of the upper branch
of the frequency-response curve appears before jumping to the
second saddle-node bifurcation. This segment can be used and fitted
into a linear equation to track the amount of mass attached on the
surface of the microbeam. Almost a 1 .mu.m jump in amplitude is
shown in FIG. 6B with V.sub.DC=3V and V.sub.AC=1.5V. This type of
response can be called a jump-down switch.
[0040] FIG. 7 illustrates an example diagram of a setup for optical
gas sensing according to various embodiments described herein. FIG.
7 shows a diagram of the setup with a high pressure nitrogen source
connected from one side to a bubbler, which contains the gas in
liquid phase, and connected from the other side to a flow meter
controller. The flow meter controller is configured to manage the
nitrogen flow when purging is needed to restore the frequency of a
microbeam device to its default value. The output of the bubbler is
connected to a second flow meter to control the flow of the gas and
the nitrogen mixture. A multifunction data acquisition card with a
Labview program, for example, is utilized to control the flow
rates. A vacuum chamber is connected to the gas setup and is placed
under a laser Doppler vibrometer in order to measure the microbeam
deflection (i.e., vibration frequency) in real time. The laser
Doppler vibrometer can be any suitable instrument, such as a
Polytec Micro System Analyzer, for example, or a similar tool for
the analysis and visualization of structural vibrations and surface
topography in MEMS micro structures. In other embodiments, any
suitable instrument can be used to analyze and measure the
structural vibrations and/or surface topography of the microbeams
described herein.
[0041] Referring again to FIG. 7, in the example cases described
below, the flow mass controller connected to the bubbler is set to
allow 0.4 L/min. and 0.1 L/min. of flow for the jump-up and
jump-down experiments, respectively. The last inlet of the vacuum
chamber is connected to a pressure gauge to measure the pressure,
which is equal to 3.3 Torr and 220 mTorr for the jump-up and
jump-down experiments described below, respectively.
[0042] Using coated microbeam devices and the test setup described
herein, a new technique to track frequency shift in the nonlinear
regime due to mass detection is described. In that context, FIGS.
8A and 8B illustrate real time measurements of a frequency response
jump before and after vapor exposure, including a jump up at 3.3
Torr and a jump down at 220 mTorr, respectively. Before taking the
vapor measurements shown in FIGS. 8A and 8B, the coated microbeam
was flushed with nitrogen to ensure that substantially all the
solvent in the HKUST-1 MOF was flushed to start with a stable
frequency reference.
[0043] The vapor sensing measurements were performed using a
relatively small frequency step to increase the accuracy of the
chosen frequency. The acquisition experiment is started using the
NI PXI acquisition card before introducing the gas to fix the
measurement reference. Then, the flow meter is fixed in order to
get the same conditions of pressure and flow rate with the
characterization measurements.
[0044] In FIG. 8A, the jump-up switch is demonstrated using real
time measurements performed upon vapor introduction at a pressure
of 3.3 Torr. The frequency response curve is shifted to a lower
range of frequency and then, at a certain point, the displacement
amplitude jumps up suddenly. This change in displacement amplitude
is proposed not just for a highly-sensitive sensor but also for
switching purposes, as described in further detail below. In FIG.
8B, the same microbeam is used, although another set of conditions
are utilized. The flow rate is set to be 0.1 L/min, which leads the
pressure of the vacuum chamber to be equal to 220 mTorr.
[0045] FIGS. 9A and 9B illustrate frequency responses before and
after gas sensing and a linear fitting of the upper branch in the
frequency response at 220 mTorr, respectively, according to various
embodiments described herein. In FIG. 9A, the nonlinear frequency
response is shown for V.sub.DC=3 V and V.sub.AC=1.5 V under a
pressure of 220 mTorr. Using this set of conditions, the cubic
nonlinearity dominates and the hardening behavior appears in the
frequency response.
[0046] Next, an approximate technique to quantify a mass captured
by a microbeam by linearly fitting the upper branch of the
frequency response curve based on the hardening behavior is
described. The concept relies on operating the resonator at a fixed
frequency f.sub.Operating before the jump down regime in the
frequency response curve. Then, at the fixed frequency
f.sub.Operating, the variation of the amplitude is tracked as the
microbeam is exposed to vapor. Essentially, the exposure to vapor
will increase the mass of the microbeam, thereby downshifting its
natural frequency and, hence, the curve in FIG. 9B to lower values.
This means that f.sub.Operating will correspond to a higher value
of amplitude in the frequency response curve. This change in
amplitude can be quantified and related/calibrated to the amount of
captured mass.
[0047] As shown in FIG. 9B, using a linear fitting, the slope of
the linear branch is determined, which represents the variation of
the amplitude with respect to the frequency |dY/df|=2.69
[.mu.m/Hz]. Exposing the microbeam to vapor leads to an increase in
amplitude. This is further clarified in FIG. 10A, which shows a
real time measurement of the microbeam mid-point deflection when
exposed to water vapor. The amplitude of the fixed frequency is
equal to before vapor exposure. After 25 seconds of vapor exposure,
the amplitude of the point before the jump (B-jump) reaches
Y.sub.B-jump=1.48 [.mu.m], then it jumps-down as shown in FIG.
10A.
[0048] The frequency shift as a function of time is important
information to be determined in the dynamic-based sensor. As the
variation of amplitude has been done in the linearly fitted regime,
the calculated slope is used to determine the frequency shift as a
function of time shown in FIG. 10B. The initial amplitude value can
be subtracted from the amplitude variation and then divided by the
calculated slope. Measuring the frequency shift as a function of
time from FIG. 10B, .DELTA.f=85 Hz was found before reaching the
jump zone.
[0049] In order to check the accuracy of the calculations, the
frequency shift coming from the real time measurement in FIG. 10B
was compared with the frequency shift calculated from FIG. 9B, by
subtracting the frequency of the point just before the jump
f.sub.B-Jump=91.045 [kHz] from the operating frequency
f.sub.Operation=90.955 [kHz]. The least calculated frequency is
found to be equal to .DELTA.f=85.55 [Hz], which is very close to
the calculated frequency shift using linear fitting.
[0050] Using Eq. (2), the amount of the added mass can be tracked
in real time from the induced frequency shift shown in FIG. 10B.
The total mass attached on the sensor before the activation of the
switch is .DELTA.m=.sup.1.DELTA.f=395 [pg].
[0051] In order to verify the stability of the selected frequency,
a noise analysis is performed at 200 mTorr pressure using
electrical characterization. Due to the AC voltage limitations in
the impedance analyzer, the value of V.sub.AC was set equal to 1V
instead of 1.5V. The same DC voltage has been selected of the gas
experiment. The frequency responses of the microbeam at the
above-mentioned conditions are plotted in FIGS. 11A and 11B. The
phase slope of the linear branch in FIG. 11B is determined to be
|d.PHI./df|=0.00169 [.degree./Hz].
[0052] The phase evolution in time is performed for different
operating frequencies in order to investigate the most stable
frequency range. FIGS. 11C-11E illustrate noise analysis graphs,
including variation of phase at a fixed frequencies of 91.11 kHz,
91.17 kHz, and 91.21 kHz as a function of time, respectively. In
FIGS. 11C-11E, the phase variation is determined to be equal to
d.PHI.=0.139.degree., d.PHI.=0.14.degree., and d.PHI.=0.12.degree.
for the operating frequencies of 91.11 kHz, 91.17 kHz, and 91.21
kHz, respectively. Using the calculated slope, the frequency shifts
due to noise are determined to be 79.88 [Hz], 82.84 [Hz] and 71
[Hz] for the phase variations in FIGS. 11C-11E, respectively. Based
on the previous frequency stability investigation, the stable zone
is demonstrated to be within almost 80 [Hz] from the jumping
frequency 91.22 [kHz] to successfully perform the switching
operation.
[0053] In other aspects of the embodiments, a new switching
technique is described based on the nonlinear response of the
microbeam outlined above. Two kinds of switches have been
introduced previously, and the jump-down switch mechanism is
described next. To demonstrate the jump-down switch, a
microcontroller is electrically connected to the gas sensing setup,
and it should be appreciated that any suitable microcontroller can
be used. The output from the data acquisition (e.g., the
vibrometer) is connected to the microcontroller. A C++ or other
suitable program is developed to read the voltages or other signals
coming from the laser doppler vibrometer at a fixed frequency. The
algorithm is based on calculating the amplitude difference between
two successive points during a frequency sweep. When the absolute
value of the difference between the current and previous data point
exceeds a defined constant, switching is triggered.
[0054] FIG. 12 illustrates a real time measurement and
corresponding light emitting diode (LED) trigger according to
various embodiments described herein. As noted above, an LED can be
connected to a digital output of the microcontroller to indicate
the switching upon gas adsorption. As shown in FIG. 12, the output
voltage of the LED is tracked in a separate waveform. When the jump
occurs, the voltage rises from 0 to 5V, which represents the
switching phenomenon.
[0055] FIG. 13 illustrates another real time measurement and
corresponding light emitting diode trigger according to various
embodiments described herein. In the context of FIG. 13, it is
noted that one of the most important characteristics of a switch is
its rise time response, which is the required time to change from
one state to another. The rise time of the switch studied herein is
T.sub.1=3.4 [.mu.s], which is the speed of the output pin of the
microcontroller. The value of T.sub.1 is related only to the
microcontroller performance, which is responsible to send the
action upon exceeding certain threshold. Another constant can be
determined from FIG. 13, which is related to the microbeam and the
implemented algorithm is found to be equal to T.sub.2=51.4 [.mu.s]
for an amplitude difference equal to dY=0.1 [.mu.m]. This time
constant reveals how much time is needed to send the information
from the switch to the controller. Thus, the total time required to
execute an action using the proposed switch is almost
T.sub.total=55 [.mu.s]. This time value can be minimized using a
more optimized algorithm in order to detect lower jump distance.
Scaling the microbeam resonator down will also lead to a faster
switch and more sensitive electronic nose.
[0056] Aspects of the embodiments can be performed or executed by
processing circuitry, including one or more microcontrollers,
microprocessors, and/or general purpose computers. The processing
circuitry can include one or more processors, Random Access
Memories (RAMs), Read Only Memories (ROMs), other memory devices,
local and/or area networks and interfaces, and an Input Output
(I/O) interfaces.
[0057] The processors can comprise any suitable general purpose
arithmetic processor and/or processing circuitry. The RAM and ROM
can comprise any suitable random access or read only memory devices
that store computer-readable instructions to be executed by the
processor. Similarly, the memory devices can store
computer-readable instructions thereon that, when executed by the
processor, direct the processor to execute various aspects of the
embodiments described herein. As a non-limiting example group, the
memory devices can comprise one or more of an optical disc, a
magnetic disc, a semiconductor memory (i.e., a magnetic, floating
gate, or similar semiconductor-based memory), a magnetic tape
memory, a removable memory, combinations thereof, or any other
known memory means for storing computer-readable instructions.
[0058] In some embodiments, one or more of the processors can
comprise an Application Specific Integrated Circuit (ASIC), Field
Programmable Gate Array (FPGA), state machine, or other
specific-purpose or embedded processing circuitry. In that case,
the processes described herein can be executed by the
specific-purpose circuitry according to an embedded circuitry
design, by firmware, by the execution of computer-readable
instructions, or a combination thereof.
[0059] In one aspect, among others, a system comprises a
microelectromechanical system (MEMS) microbeam device; an
instrument to measure structural vibrations of the MEMS microbeam
device over time; and a processing circuit coupled to the
instrument and configured to: conduct an analysis of the structural
vibrations of the MEMS microbeam device; and detect a change in a
response behavior of the MEMS microbeam device based on the
analysis. In one or more aspects, the MEMS microbeam device can be
coated with a Metal-Organic Framework (MOF) layer. The MOF layer
can comprise an HKUST-1 MOF layer. The change in the response
behavior of the MEMS microbeam device can comprise a mass-induced
change in the response behavior. The MEMS microbeam device is
operated at an operating pressure and at an operating voltage to
induce at least one of a softening nonlinear response behavior or a
hardening nonlinear response behavior of the MEMS microbeam
device.
[0060] In one or more aspects, the processing circuit can be
further configured to track a frequency response of the structural
vibrations of the MEMS microbeam device over time. The processing
circuit can be further configured to quantify a mass captured by
the MEMS microbeam device based on a frequency shift of the
structural vibrations of the MEMS microbeam device over time. The
processing circuit can be further configured to trigger a switch
based on a difference in a frequency response of the structural
vibrations of the MEMS microbeam device over time.
[0061] In another aspect, a method comprises operating a
microelectromechanical system (MEMS) microbeam device at an
operating pressure and at an operating voltage; measuring
structural vibrations of the MEMS microbeam device over time;
conducting an analysis of the structural vibrations of the MEMS
microbeam device; and detecting a change in a response behavior of
the MEMS microbeam device based on the analysis. In one or more
aspects, the MEMS microbeam device is coated with a Metal-Organic
Framework (MOF) layer. The MOF layer can comprise an HKUST-1 MOF
layer. The change in the response behavior of the MEMS microbeam
device can comprise a mass-induced change in the response
behavior.
[0062] In one or more aspects, the method can further comprise
operating the MEMS microbeam device to induce at least one of a
softening nonlinear response behavior or a hardening nonlinear
response behavior of the MEMS microbeam device. The method can
further comprise tracking a frequency response of the structural
vibrations of the MEMS microbeam device over time. The method can
further comprise quantifying a mass captured by the MEMS microbeam
device based on a frequency shift of the structural vibrations of
the MEMS microbeam device over time. The method can further
comprising triggering a switch based on a difference in a frequency
response of the structural vibrations of the MEMS microbeam device
over time.
[0063] In another aspect, a method comprises forming a sacrificial
layer over at least one lower electrode, the sacrificial layer
comprising anchor passages extending through the sacrificial layer
to the at least one lower electrode; forming an upper electrode on
the sacrificial layer, the upper electrode contacting the lower
electrode through the anchor passages; forming a structural layer
on the upper electrode; forming a protective layer on the
structural layer; removing the sacrificial layer to release a
microbeam comprising the upper electrode, the structural layer and
the protective layer, the microbeam suspended by anchors defined by
the anchor passages; and coating the microbeam with a Metal-Organic
Framework (MOF) layer. In one or more aspects, the upper electrode
can comprise a first chromium layer, a gold layer disposed on the
first chromium layer, and a second chromium layer disposed on the
gold layer. The lower electrode can comprise a chromium layer and a
gold layer. The structural layer can comprise polyimide. The
protective layer can comprise nickel. The MOF layer can comprise an
HKUST-1 MOF layer.
[0064] In addition, all optional and preferred features and
modifications of the described embodiments are usable in all
aspects of the disclosure taught herein. Furthermore, the
individual features of the dependent claims, as well as all
optional and preferred features and modifications of the described
embodiments are combinable and interchangeable with one
another.
[0065] Disjunctive language, such as the phrase "at least one of X,
Y, or Z," unless specifically stated otherwise, is to be understood
with the context as used in general to present that an item, term,
etc., can be either X, Y, or Z, or any combination thereof (e.g.,
X, Y, and/or Z). Thus, such disjunctive language is not generally
intended to, and should not, imply that certain embodiments require
at least one of X, at least one of Y, or at least one of Z to be
each present.
[0066] It should be emphasized that the above-described embodiments
of the present disclosure are merely possible examples of
implementations set forth for a clear understanding of the
principles of the disclosure. Many variations and modifications may
be made to the above-described embodiment(s) without departing
substantially from the spirit and principles of the disclosure. All
such modifications and variations are intended to be included
herein within the scope of this disclosure and protected by the
following claims.
* * * * *